The human body is made up of trillions of cells that grow, divide into new cells and then die in an orderly manner. When we’re young, cells divide quickly to allow for growth, and when we become adults, cells most commonly divide only to replace worn-out or dying cells or to repair an injury.Cancer – the general name given to a group of more than 100 diseases – begins when cells in part of the body start to grow out of control. Instead of dying, cancer cells continue growing and forming new, abnormal cells. Cancer cells can also invade other tissues within the body, something that normal cells cannot do.Why do cancer cells do what they do? Damage to DNA – the instructions encoded in every cell. In normal cells, damaged DNA gets repaired or the damaged cell dies.Cancer cells, however, aren’t repaired, and the cell doesn’t die like it should. Instead, the cell continues making new cells that the body doesn’t need, all with the same damaged DNA. In most cases these cancer cells begin to form a tumor (commonly referred to as a mass or a lump).Differences in our DNA make us unique, and they are also the reason there is no routine cancer. Our genetic differences mean that each person’s cancer is different, which means that each person’s treatment and outcome will be different as well.Visit cancer.osu.edu to learn more about cancer, including how it begins and what causes it.